Frankfurt an der Oder, Germany — When Poland's right-wing Law and Justice Party came to power last month in national elections, many, particularly in Germany, saw it as a bad omen.

After all, when the Euroskeptic party, known as PiS, governed Poland from 2005-07, party leader and then-Prime Minister Jarosław Kaczyński made no secret of his staunchly anti-German views.

Back then, he demanded extra voting representation in the EU for his country to make up for the number of Poles killed by the Nazis in World War II, and accused Berlin of plotting to reclaim areas in western Poland that once belonged to Germany. Mr. Kaczyński even suggested that German Chancellor Angela Merkel came to power with the aid of the East German secret police.

And while Kaczyński is not leading the country this time – new Prime Minister Beata Szydło was sworn in on Monday – he is still widely thought to be extremely influential. Many in Germany and Poland worry that PiS's sweep to power could revive historical grudges.

But a visit to the sister cities of Germany's Frankfurt an der Oder and Poland's Słubice shows just how far Germans and Poles have moved beyond old resentments.

Wars, contested borders, and economic disparity once made bitter enemies out of residents on each side of the marshy Oder River. But following Poland’s entry into the European Union and the subsequent dismantling of borders, the twin cities have emerged as a symbol of German-Polish reconciliation and European unity. And locals aren't keen to return to old prejudices.

“The transformation at this border has been nothing short of a political and social miracle,” says Krzysztof Wojciechowski, a professor at the European University Viadrina, whose campus is situated in both cities. “We were total enemies living under the conditions of great asymmetry, who have managed to overcome our mutual fears to forge new new ties and establish unprecedented cooperation.”

A history of distrust

Słubice was part of Frankfurt until Hitler’s defeat in 1945, when the victorious Allies redrew Germany’s eastern border along the Oder River, handing Poland nearly 40,000 square miles of long-German land. Millions of ethnic Germans were expelled from their homes, replaced by new Polish settlers.

During the Soviet era, Poland and East Germany became official allies, but residents of Frankfurt and Słubice remained deeply suspicious of each other and movement between the two cities was restricted.

When the Berlin Wall fell in 1989, so too did the barriers across the Oder. But the relations were largely transactional: Germans would cross over to Poland to stock up on cheap cigarettes and gasoline, while Poles would buy higher quality products in Germany.

“It was terrible in those days,” recalls Victor Walentynowicz, who spent nearly two decades working as a border control guard in Słubice until Poland officially joined the European Union’s borderless zone known as the Schengen area and the checkpoints were dismantled in 2007. “The Germans looked down on us or thought we would come take their jobs. And to be honest, we weren’t so fond of them, either.”

'I don't feel any border anymore'

Today, however, Polish and German children attend a bilingual kindergarten in Frankfurt, which promises a “childhood without borders.” Frankfurt and Słubice now pool some municipal services, including heating and waste-water treatment. And for the first time since World War II, jointly operated public transportation connects the two urban centers via cross-border bus No. 983.

Perhaps the biggest catalyst for change has been European University Viadrina, a German institution that was re-established in 1991 as a joint project with Poland with the aim of bridging the chasm between east and west. According to spokesman Lars Weber, 6,500 students — a quarter of whom come from abroad, including 650 Poles — attend courses on campuses in both Frankfurt and Słubice. “It is a truly international university that embodies the spirit of European integration,” he says.

Professor Wojciechowski came to the border town from Warsaw in 1991 to help set up Viadrina’s Słubice facility.

“Back then, at first sight you could recognize who is Polish or German by different behavior, different dress, different cars,” Wojciechowski says. “Now almost all of these differences have disappeared.”

Bart Wieczorek, who is studying for a master’s degree in intercultural communications at Viadrina, remembers a time when being Polish in Germany was a source of embarrassment.

“Before Poland joined the EU, my friends would always say, 'don’t speak Polish in Germany,' because the stereotype of Poles back then was drug dealer, car stealer, gangster,” he says. “I grew up in the western part of Poland that used to be German, and there was a lot of prejudice on that side as well, especially among the older people who were not sure if the Germans were going to come back.”

“But I don’t feel any border anymore,” adds Mr. Wieczorek, who serves on a student committee for urban policy and Polish-German relations.

A break from the past

To be sure, he says, bad blood could reemerge in the wake of Poland’s political shift.

“I’m not responsible for the policies of my country, but the [PiS] promotes this idea that Poland is like a victim of history — that everything is Russia’s fault or Germany’s fault,” Wieczorek says. “A lot of [Polish] people buy into this idea. There’s resentment on the German side, too, and I just worry these voices will drown out the progress that we’ve made.”

But locals are confident that they can maintain the positive relations, whatever PiS does.

“We have to break the idea of the border in our minds,” says Charlotte Ciesielski, a German student at Viadrina. “There’s a big difference between the politicians and the people — if we want to maintain contact, we will do it independently of whatever the politicians do.”